Corrosion inhibiting composition containing arsenous oxide and potassium hydroxide



April 21, 1953 Filed Dec. 22, 1951 H. ho coRRosIoN INHIBITI HRBACK FAI; NG COMPOSITION CONTAINING ARSENOUS OXIDE AND POTASSIUM HYDRDXIDE 2 SHEETS- SHEET 1 G/LSON H. ROHRBACK DW/TE M. MCCLOUD W/LLARD R, SCOTTJ/ April 21, 11953 G. H. ROHRBACK ETAL 2,635,999

CORROSION INHIBITING COMPOSITION CONTAINING ARSENOUS OXIDE AND POTASSIUM HYDROXIDE G/LSON H. ROHRBACK DW/TE M. MCCLOUD W/LLARD R SCOT* J/r Patented Apr. 21, 1953 2,635,999- I C E CORROSION INHIBITING COMPOSITION CONTAINING ARSENOUS OXIDE AND POTASSIUM HYDROXIDE Gilson H. Rohrback, Whittier, Dwite M. McCloud,

Buena Park, and Willard R. Scott, Jr., Alhambra, Calif., assignors to California Research Corporation, San Francisco, Calif., a corporation of Delaware Application December 22, 1951, Serial No. 262,994

13 Claims. 1

This invention relates to a corrosion inhibitor for use in inhibiting the corrosion of ferrous metal piping and tubing in producing wells and in pipe lines transporting crude oil. More particularly, it relates to a solid arsenous corrosion inhibitor.

The corrosion of ferrous metal tubing and piping in producing oil wells and in pipe lines transporting crude oil is now and has for some years been a serious operating problem confronting the petroleum producer. Corrosion of tubing and piping necessitates frequent interruptions of production to pull corroded tubing and piping from the Well and replace them with new material.r The essential features of a corrosive environment very commonly encountered in producing oil Wells, and `one in which the corrosion inhibitor of this invention is highly effective, in`

clude a ferrous metal in contact with oil, brine, and gas containing carbon dioxide, gas liquid interfaces in contact with the metal, and areas of turbulent liquid flow in contact with the metal Isurfaces. The metal in this environment is corroded away by direct attack of carbonio acid which is greatly accelerated by electrochemical phenomena arising out of the contact of the phase interfaces with the metal and out of the contact of turbulent flowing liquid with the metal surface. Substantially all of the acidity of the production stream stems from the presence of ,carbon dioxide. The acidity is quite low, the pI-I not being lower than 3 and being ordinarily in the range 4 to 6. When a ferrous metal is exposed to the production effluent under quiescent conditions where there is no movement of the 'liquid or of free gas bubbles through the liquid, lthe corrosion rate observed is usually less than about 25% of that observed under actual producing conditions which include turbulent motion of the liquid in contact with the metal and the presence of minute gas bubbles which contact the metal. In laboratory apparatus in which the separate influence of the three corrosive factors was studied, i. e., direct acid attack, electrochemical attack attributable to turbulent liquid flow, and electrochemical attack attributable to lthe presence of finely-divided gas bubbles which contact the metal surfaces, it was found that the relative rate of corrosion due to direct acid attack Was 4 units, and that the relative rate cf ycorrosion when either theV condition of liquid turbulence or finely-divided gas bubbles moving through the liquid was superimposed on the presence of the acid medium, the relative corrosion rate immediately increased to 14 units. From these' observations it is clear that the corrosion problem would not be solved by the employment of an inhibitor which would eliminate only the corrosive action due to direct acid attack and that the corrosion problem here presented can be solved only if the additional electrochemical corrosion attributable largely to physical conditions is markedly reduced. The corrosion inhibitor of this invention is especially Well adapted to minimizing the corrosion of ferrous metals in the environment and by the mechanisms described.

A variety of physical setups is found in producing oil wells which determine the manner of introduction of the corrosion inhibitor into the Well. Some wells have open annuli and a corrosion inhibiting solution can be lubricated into the well through the open annulus. Some Wells have packed-off annuli and the corrosion inhibitor must be introduced through the production tubing by pumping an inhibitor solution to the well bottom and permitting it to flow upward with the production stream or by dropping a solid corrosion inhibitor through the tubing to the well bottom and producing the well. In condensate Wells, where there is no liquid production stream, the corrosion inhibitor to be effective must in some manner be applied to the interior surface of the tubing without the aid of a liquid production stream to carry and spread it.

A solid corrosion inhibitor Which can be placed at or near the well bottom by dropping it through the Well tubing can be utilized effectively in all types of Wells if the solid inhibitor has the following properties: First, it must be an eective inhibitor at low concentrations. Only relatively small amounts of an inhibitor can be introduced into a well bydropping the solid inhibitor through the tubing. Some commonly used inhibiting chemicals such as dichromates and caustic soda will inhibit satisfactorily if used in large amounts, but these materials are not suitable for injection into the Well in solid form since the maintenance of the desired concentration requires very frequent interruption of the production for the introduction of further amounts of the inhibitor. A suitable chemical inhibitor for injection into the well through the tubing in solid form would be one that provides protection against corrosion at concentrations of about one to ve parts per million in the produced water. Second, an effective solid corrosion inhibitor should have a high persistency in its inhibiting effect. To be practical, the injections of a solid inhibitor should not be made more often than once in twentyfour hours, and preferably once in several days, or once a Week. High persistency of the inhibitor or inhibiting film formed on the metal surfaces of the tubing is highly desirable in solid inhibitor injection. Third, a successful solid corrosion inhibitor should be highly soluble in well Water. This is particularly desirable if the inhibitor is to be used in a condensate well. Relatively insoluble or highly insoluble materials could easily cause plugging of the tubing.

Fourth, a solid corrosion inhibitor should. have hydroxideluthe composition when tho Water cona high density so that the solid inhibitor will fall tent is approximately constant. The composithrough the production stream While the Well is i vtions are designated soft when they are readily being produced. If the solid inhibitor has this molded by manual pressure.

property, the production need be interrupted for 5 The properties of arsenous oxide-potassium only the few minutes necessary to introducel the hydroxide-Water mixtures were further studied solid into the tubing. Fifth, the solid inhibitor, to determine the range of compositions which if it is to be effective in a condensate Wel-l, should produced hard products at atmospheric temperasoften at or slightly below the temperature exlstture.

ing at the Zone of condensation. Condensatie 1,0 From' these studies it was determined that the wells produce little or no formation Water and ratio by Weight,r of' arsenous oxide to potassium much of a. water-soluble chemical that falls below hydroxide in compositions having softening the condensate zone will not be returned with points above 100 F: lie in the range from 1.8:1 the production. If the solid inhibitor softens or' v to 5:1 and that the water content should be from melts at temperatures from about 150 to 200 F., 15 1 to 3.0 parts by Weight to each 15 parts'- by the solid will be spread oiithe hot tubing wall as weight of arsenous oxide and potassium M itfalls inthe well. dioxide together. Compositions having softening. Arsenous compounds, particularly the alkali points aboveloe mmust contain Asco; and Kon metal arsenites or .Sluliies of arsenous oxdewith at .Weightfatios` in the range 3;; t@ ,254 and alkali metal baldi-oxides and water, meet the 2 0 oompositionshavinehigher softening points espef above-described requirements with respect to cially useful when placed at the bottom of average effectiveness at low concentration. pBrSiSellCe, producing Wells Where high temperatures exist and solubility admirably. Particular arsenous should have Ascot to KOH weight ratios in the compositions hereinafter described moet not only ,range from. l225:1 to 30:1. Representative cbthe first three requirements, but also the reduireservations are set out` in the following Table Il.

Table II Set Consistency softening Temp.. QF..

ments withv respect to density and to softening 25 From the table it is clear that the character of point in a remarkable manner. they compositions changes abruptly when thear It has now been found that a lia-rd, dense senous' oxide to potassium hydroxide ratio goes homogeneous's'olid corrosion inhibitor can be preah'ove about 1.7511 and that the softening pared by intimately mixing arsenous oxide, potemperature falls off as the ratio approaches tassium. hydroxide and. water and cooling the 5:1. Thel softening temperature of the solid I resultant mixture to remove exothermio heat of AszOae-KOH-Hzo compositions is effectednot reaction. The mixture contains from vl to 3.0 only bythe' ratio of arsenous oxide-to potassium 1 parts by weightof water to-15 parte by Weight of hydroxide, butA also by the amount of water coli f potassium hydroxide and arsenous oxide together tained in the composition. In genera-l,v the come and the ratio of arsenous oxide to potassium: hypositions soften` at lower temperatures as the cli-oxide in the mixture isvv in the range 1.8.:1 tu5z1.. 45 water content'- of. the composition rises. The v An organic hydroxy compound such asethylene minimum Water content for practical purposes-is glycol and other similar materials set forth here l-'part by weight ofwater to 15 parts' by Weight inaf'ter is desirablysubstituted for part of the ofv arsenous oxide; and potassium hydroxide tolwater in the composition. gather. When it is: attempted` to employ smaller Compositionsl containing these ingredients` in `59 amounts of water', it is extremely difficult to make these proportions. are very hard atv ordinary tema homogeneous mixture of the three components peratures, have a high density above about 3.0 e. before the partially mixed materials set. If. more per cubic centimeter and are thermoplastic in the than 3.0 parts by weight of water to 15. palm,` by sense that theybecome soft at temperatures from Weight of arsenous oxide and. potassium by... about 150` to about 280 F., and finally become .5:5 dioxide combined are employed. the'compooitions liquid at higher temperatures. are dentely Soft al;l 100 F. and remain softer Numerous' compositions,v consisting essentially liquid at that temperature'. Compositions have of arsenous oxide, potassium. hydroxide. and water ing softening points above 150q F. should contain were prepared and their properties at atmosno more than 2.5 parts by weight of water for pheri'c temperaturewere examined.. The compos 3 9 each 15 Darts by Weight of arsenous oxide-and sition vand properties of several of these mixtures DOCaSsium hydroxide together and Should contain are summarized in Table I; at leastl part by weight of water to each: 15 Table I ports by weight of arsenous oxide and. botas'. 1 4 slum hydroxide together to permit adequate mixing before settingA occurs.. Compositions hay. ins higher softening points above 200 F. which are especiallyv useful when placed at the bottom ggoigigxglbfel 2.0 of .producing wells wherel high temperaturespro- Set Qonsl'stoiiey.. Soft..T Soft.--

Vall .Should Contain not more than 2-.25 pari-,g By

. .....K E weight of water for each 15k parts by weight of rute .1 o t" ,15b i-htfHo. e v' From the im inf the above tab-ie it is clear oomoositionsis illustrated by Figure'i or the that room temperature, hardness clearly redrawing-is,4 which is a-eranhical representation of late@ to the ratio of arsenousoxide.topotassium 't5 theA variation of softening temperature with Water content When varying amounts of Water are added to parts by Weight of arsenous oxide and potassium hydroxide. The ratio of arsenous oxide to potassium hydroxide in the experiments providing the data for the construction of Figure l'was 2.33z1.

From Figure 1 it is evident that the softening point of the compositions can be varied from 150 F. to 290 F'. by varying the water content.

16 forms suitable for introduction into the well. The substitution of ethylene glycol for a part of the water in the inhibitor compositions also increases the resistance of the solid product to shearing and impact forces. When water alone is used. the solid tends to be somewhat -grainy and brittle and, when it is cast in stick' form, the stick may be rather readily broken by shearing or impact forces. This characteristic is For example, a solid inhibitor composition hav- 10 undesirable if it is intended to drop the solid ing a softening point of about 280 F. would be inhibitor in stick form into the Well tubing. The best suited for use in the high pressure flowing sticks strike against the tubing as they falland Wells of Louisiana, where bottom hole tempermay be broken into small pieces which are caratures may be as high as 260 F., Whereas a solid ried up by the production stream before reachinhibitor composition softening at about 180 F. 15 ing the well bottom. would be well suited for use in the condensate The compositions of several solid inhibitors in wells of West Texas. In the condensate wells it which varying amOuntS Of Water Were replaced is desirable that the solid inhibitor soften sufby ethylene glycol are shown in Table III.

Table III Parts by weight A5203 Parts by Weight KOH.

Parts by Weight H2O Parts by weight Ethylene Glycol. .63

Parts by Weight Total Liquid 31 Ease of Mixing Pourable after Complete Mixing Yes Yes Yes Yes.

softening Temperature 270290 F..- 270-290 F... 270-290" F..- 270-290" F.`

ciently in the tube so that the inhibitor will rub off on the hot tubing as the solid falls in the well.

The softening point of the solid compositions may also be regulated, though less l reliably, by substituting sodium hydroxide for a small part of the potassium hydroxide. From 0.1% to 5% by weight of the potassium hydroxide may be replaced by sodium hydroxide and the softening point of the composition is lowered. When sodium hydroxide is used to regulate the softening point, care must be exercised that the amount be kept small since it exercises extraordinary effects on the softening point, so much infact that vwhen mixtures, each of which would set hard at atmospheric temperature, are combined before setting, the combined mixture remains permanently liquid.

The solid AszOa-KOil-HaO inhibitor compositions above described may be improved in two respects by substituting an organic hydroxy compound such as ethylene glycol for a part of the Water. The substitution of these materials for part of the Water very considerably reduces the rate at which the compositions set up as hard solids when the three ingredients are mixed. When arsenous oxide, potassium hydroxide and Water are mixed in the proportions above described, they tend to set very rapidly. This characteristic gives rise to a serious problem in commercial production of the inhibitor compositions Where it is desirable to mix large batches of the inhibitor and pour the mixture into molds to set. The setting is so rapid that the compositions set up as solids in the mixing vesel before pouring can be completed. The substitution of ethylene glycol for part of the Water greatly reduces the setting rate and thus facilitates com- 4,merpial production of the solid .inhibitorcast in All of the compositions shown in the table were readilypourable after complete mixing andv no difficulty was experienced in making the mixture and pouring it from the mixing vessel to casting molds without solidii-lcation occurring in the mixing vessel. The resultant sticks were much less brittle and more diicult to fracture than were corresponding compositions in which all of the liquid was water. The softening temperatures of the compositions are not adversely affected by the substitution of the ethylene glycol. If appreciable improvement in the solid is to be achieved, at least 10% by Weight of water should be replaced by ethylene glycol and usually 20 to 50% of the Water is replaced by ethylene glycol where greater durability and slower setting time are desired. The preferred organic hydroxy compound for use in the inhibitor compositions is ethylene glycol. However, it has been determined that other organic hydroxy carbon atoms per molecule, diethylene glycol and triethylene glycol produce similar effects on the setting time and resistance to fracture of the inhibitor compositions.

The inhibitor compositions above described are desirably cast in the form of pellets or sticks. The most usual form is a cylindrical stick from 1 to 3 feet in length and from 1 to 2 inches in diameter, that is, a diameter generally adapted to permit the fall of the stick through conventional Well tubing. The sticks ordinarily weigh from 1 to 10 pounds and have a density above about 3 g. per cubic centimeter. Their mass an'd density are such that they readily fall through the production stream of the average producing Well so that the production need be interrupted only for the few minutes which are required to introduce the stick into the well tubing. The introduction of such a stick every three to ten days Will ordinarily bring the corrosion rate of a Well down to an acceptable low level and maintain it there.

Since the arsenical compounds are poisonous, the sticks are desirably wrapped or coated with some non-toxic material in the interest of safe 7 handling. I.illie wrapping or coating may be 1eitlier functional or nonftiindtional .and may be andntegral part ofthe stick as it is .droppedinto fthe-Well, lor may he -nemoyable at .the time of injection.

-When the Well te be treated is -a .drawing Well ,tiredness-ing a production strewnl or oil, brine and carbon dioxide, a metal .a standard oxiadation reduction potential above 43,5 Yand below .2.'5' 1volts, {sd-ch as magnesium, aluminum, forms an excellent functional integral coating for the inhibiting .eantridges can vbe prepared by pouring --the molten corrosion tnh'ibitor into a 'thin Walled (0.01 to 0.05 inch) metal tube or [cylinder and permitting it -to :solidify there. The ends of `the tube or top-of 'the cylinder-ane then closed. The closure can be 'ma-:de by capping with a metallic cap, or crimpin-g the tubing, or sealing with a high melting point Wax or asphalt. The metalliecoating is an integra-l part of the inlnlbitor cartridge as it is dropped into the well. The metal teasing prevents the sol-id inhibitor stick from beingbroken during its tall through the tubing, and the metal is functional in action in ularly treated with commercially available .orf genio corrosion inhibitor sticks which .are 'rather widely used. The eiectiveness of .the corrosion inhibitors to inhibit corrosion of ferrous metal tubing was determined by observing theiron count of produced water before and after treatment. The iron count, a measure of the corrosion rate, is the .number of parts 'per .million oi iron calculated as ferrie oxide contained in the produced water as determined by the thioeyanate -colorometric method (Sco'tts Standard .Method .of .Chemical Analysis, 5th Edition, Van Nostrand, 415x59, page 486). .From Figure '2 it will be the inhibitor of the invention was markedly superior to Yan inhibitor .currently .inoommercial use, leven when used in very much .smaller onantities 1. A hard, dense solid comprising an intimate mixture of arsenous oxide, potassium hydroxide and Water, the .ratio by Weight of arsenous oxide to potassium hydroxide being in the range from 1.811 to 5:1 and the water content being at least :one part by weight and not more than about 3.0

the Well and not .merely acontainer tor the .in-

hibitor'. Magnesium for example, slowly vdissolves 'in 'dilute carbonio acid conttuined in theweli water and, in dissolving, neutralizes part of the acid; addition, metals'such as magnesium, zinc, aluminum their alloys provide cathodic iprotectionaganst 'eiectrolytic corrosion.

@Mother integral coatings which 'are non-functonal may be employed such as a high melting point Wax or an oil-soluble or yWater-soluble plas- Stic-material. 'The 'solidiiied inhibitor 'stick can )be vdipped in 'these materials and allowed to dry vandthe surface iilm of these materials "provides protection to `personnel agah'ist'handlinghazards In the* Well the protective coating is rapidly disjsolyed, placing the 'inhibitor composition in conljjtaot With the production stream.

'The inhibitor'sticks 'may `also be :protected by an outer 'container which is .removed prior` to the -in'trocmc'tion of the 'inhibitor stick into the well. 'The "hotsoft corrosion inhibitor "is poured into paper 'cylinders and allowed to' solidify there. Thepalier tubing isrpeeled away from `the stick .fb'efo're 'dropping it into the well It has ,LT-been "found that .if the hot corrosion inhibitor 'mixture .is poured into untreated paper tubes, ,.sdme diiliculty is experienced in attempting .to remove the paper from the hardened stick. However, if the paper is greased with a fairly heavy grease, or. covered with a water-impervious coatsuch as shellac or plastic, prior to the intro- ".duotion of the molten inhibitor composition into 'the paper tube, the paper may easily he removed lfroni the solidified stick.- Alternatively, the inolften inhibitoroan be poured into a rubljier lcylinder and allowed to solidify there. When the '.'inhibitor is solid, the top of the rubber cylinder pressed together and .sealed wth robber cement.

The corrosion inhibitors of this invention have y.to..ixiii-.istien of .the test4 :this :well was being regparts by Weight to each 15 parts by weight of :arsenous `oxide plus potassium hyroxlde.

'2. .A hard, dense solid consisting essentially of a 'reaction product of arsenous oxide, potassium hydroxide and water, the proportions of the rehydroxide and water, the 1proportions ofthe reactants being such that the ratio by Weight-of AszOa to KOH is in the range 2:1 to 425:1 and that from 1.0 to 2.25 parts 'by 'weight oi Water are present for each y15 parts by Weight of sar- -senous oxide plus potassium hydroxide. y

4. A hard, dense solid formed byvnitimately `n1ix'1ng15 parts by. Weight of arsenous oxide and potassium hydroxide with 1 to 3.0 parts byweight of Water and ethylene glycol, 4the vratio of'arsenous oxide to potassium hydroxide being in the range 1.8:1 to 5:1 and the ratio of water to .ethfylene being in excess of 1 to 1.

5. A hard, dense solid formed by mixing 10 to 12.5 parts by Weight of arsenous oxide, .2.5 to v5 parts by weight of potassium .hydroxide and 1 to about`3 parts by weight of water, the arsenous oxide and potassium hydroxide totaling l5 parts by weight.

6. A hard. dense solid formed by mixing 10 to 12 vparts by weight of arsenous oxide, 3 'to 5 parts by Weight of potassium hydroxide and v1.0 to about 3.0 parts by weight of water, the arserious oxide and potassium hydroxide totaling .15 parts by weight..

7. A hard, dense solid formed by mixing 10 to 12.5 parte by rws/eight of arsenous oxide. 2.5 to 5 parts by weight of potassium hydroxide and 1 to 3.0 parts by weight of a mixture or water .and ethylene glycol.

8. The composition as defined in claim "I, wherein the -mixture of ethylene glycol .and water contains about 10% by weight of ethylene glycol.

9. The method as defined in Aclaini 7, wherein the mixture of ethylene glycol .and water oon- .tains from 10 to 50% by weight of ethylene glycol.

10. A hard. dense solid containing 1o to .12 :parte by weight of arsenous oxide, 3 to 5 parte wherein the mixture of water and ethylene glycol 5 contains 10 to 50% by Weight of ethylene glycol.

12. The method of inhibiting corrosion in a producing oil Well delivering a production stream comprising petroleum, brine and carbon dioxide gas which comprises periodically interrupting 10 the production, dropping a solid corrosion inhibitor formed by intimately mixing arsenous oxide, potassium hydroxide and Water, the ratio by Weight of arsenous oxide to potassium hydroxide in the mixture being in the range from 1f 1.8:1 to 5:1 and the Water content of the mixture being at least one part by weight and not more than about three parts by weight to each fteen parts by Weight of arsenous oxide plus potassium hydroxide, through the well tubing to 20 the bottom of the Well and producing the well.

13. A composition as dened in claim 4, wherein the content of water and ethylene glycol is in the range from 1 to 2.5 parts by weight.

GILSON H. ROI-IRBACK. DWITE M. MCCLOUD. WILLARD R. SCOTT, JR.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 1,638,710 Sherbino Aug. 9, 1927 1,877,504 Grebe et al Sept. 13, 1932 OTHER REFERENCES J. Mellor-Comprehensive Treatise on Inorganic and Theoretical Chemistry"vol. IX- 1929, page 117. 

1. HARD, DENSE SOLID COMPRISING AN INTIMATE MIXTURE OF ARSENOUS OXIDE, POTASSIUM HYDROXIDE AND WATER, THE RATIO BY WEIGHT OF ARSENOUS OXIDE TO POTASSIUM HYDROXIDE BEING THE RANGE FROM 1.8:1 TO 5:1 AND THE WATER CONTENT BEING AT LEAST ONE PART BY WEIGHT AND NOT MORE THAN ABOUT 3.0 PARTS BY WEIGHT TO EACH 15 PARTS BY WEIGHT OF ARSENOUS OXIDE PLUS POTASSIUM HYDROXIDE.
 12. THE METHOD OF INHIBITING CORROSION IN A PRODUCING OIL WELL DELIVERING A PRODUCTION STREAM COMPRISING PETROLEUM, BRINE AND CARBON DIOXIDE GAS WHICH COMPRISES PERIODICALLY INTERRUPTING THE PRODUCTION, DROPPING A SOLID CORROSION INHIBITOR FORMED BY INTIMATELY MIXING ARSENOUS OXIDE, POTASSIUM HYDROXIDE AND WATER, THE RATIO BY WEIGHT OF ARSENOUS OXIDE TO POTASSIUM HYDROXIDE IN THE MIXTURE BEING IN THE RANGE FROM 1.8:1 TO 5:1 AND THE WATER CONTENT OF THE MIXTURE BEING AT LEAST ONE PART BY WEIGHT AND NOT MORE THAN ABOUT THREE PARTS BY WEIGHT TO EACH FIFTEEN PARTS BY WEIGHT OF ARSENOUS OXIDE PLUS POTASSIUM HYDROXIDE, THROUGH THE WELL TUBING TO THE BOTTOM OF THE WELL AND PRODUCING THE WELL. 